1. Field of the Invention
The present invention relates to an optical reader, and more particularly relates to a reader having a characteristic structure of a read-out means.
2. Description of the Prior Art
Conventionally, a linear photodiode type elongated photosensor made of a silicon monocrystal has been used in a photoelectric conversion device which is used as a read-out means of an image processing apparatus, such as facsimile, and as a character reader. The photosensor of this type however has been restricted in its length and also has been manufactured with a low yield because of the available dimensions of silicon and manufacturing precision monocrystals. For this reason, in the case of a wide original to be read out (for instance, A4 size, of 210 mm width), an original image has been focussed as a scaled-down image onto a photosensor using an appropriate lens system. However, the introduction of such scaling-down optical system results in a hardship in miniaturizing the light reception section. In addition, since a sufficiently large light reception area (pixel area) can not be obtained for each pixel, a large amount of light has been required in order to obtain a sufficient signal current. Therefore, the photosensor as above under present conditions has been used for such read-out apparatuses as a low speed type reader with a longer read-out time, or a reader of which a high resolution is not required.
Apart from the above, recently, a photosensor using amorphous silicon has been proposed. This photosensor can be implemented by forming a thin layer of amorphous silicon using a vapor deposition method. Therefore, a large dimension photosensor or an elongated photosensor can readily be obtained. With the photosensor using amorphous silicon, even an original with a large width can be read out in the same scale, enabling one to realize a tight-contact type image sensor. Thus, miniaturization of the reader can be attained.
As driving methods for such readers, a direct drive method and a matrix drive method have been proposed. The matrix drive method uses a lesser number of drive ICs so that the reader can be manufactured with a low cost. FIG. 1 is a brief partial plan view of the circumference of a read-out section of a reader using a matrix drive method, and FIG. 2 is a cross sectional view along a line II--II of FIG. 1. In the figures, numeral 1 represents a substrate, numeral 2 represents an amorphous silicon photoconductive layer mounted on the substrate, numeral 3 represents common electrodes, and numeral 4-1 represents a separate electrodes. A gap portion at which each separate electrode 4-1 faces the common electrode 3 corresponds to a pixel portion (i.e., sensor portion). In the figures, the pixels are disposed in a 7.times.5 (=35) array. The pixels are divided into 7 blocks, each block including five pixels. The common electrodes 3 are respectively provided one for each block. The separate electrode 4-1 is at the opposite side of the sensor portion and is provided with an insulation layer 5. The insulation layer 5 is formed with a through hole 6 through which each separate electrode 4-1 of the block is connected to the corresponding one of five signal pick-up wires 7 mounted on the insulation layer 5. Therefore, the photosensor array can be driven in a matrix fashion by connecting to a driver circuit the seven terminals for the common electrodes 3 and five pick-up terminals for the pick-up wires.
With the matrix drive method, although it is possible to miniaturize the drive circuit section as described above, the structure of the wiring section becomes complicated. Although a photosensor with thirty-five pixels has been described with reference to FIGS. 1 and 2, in the case of an elongated photosensor having a high density of pixels, the number of pixels becomes 1728 for example. Therefore, the structure of a multi-layer wiring section becomes quite complicated.
In conventional readers of this kind, as shown in FIGS. 1 and 2, since the read-out section and the multi-layer wiring section for matrix connection have been formed on the same substrate, the manufacturing yield of the reader equals the manufacturing yield of the read-out section multiplied by the manufacturing yield of the wiring section. As a result, the manufacturing yield of the reader of this kind has been very low, thus resulting in a high cost in manufacturing.